If you, like Toigo, define a cloud as a resource that can be dynamically provisioned -- that is, allocated and de-allocated on demand -- and made available within a company with security and good management controls, "then all of that exists already in a mainframe," he says.

Of course, Toigo's is not the only definition of what constitutes a cloud. Most experts say that a key attribute of the cloud is that the dynamic provisioning is self-service -- that is, at the user's demand.

But the controlled environment of the mainframe, and the basis for much of its security, traditionally requires an administrator to provision computing power to specific tasks. That's the basis for the mainframe's reputation as old technology that operates under an outdated IT paradigm of command and control.

That's just one of the reasons why most cloud computing today runs on X86-based distributed architectures, not mainframes. Other reasons: mainframe hardware is expensive, licensing and software costs tend to be high as well, and there is a shortage of mainframe skills.

Big iron, meet cloud

Nevertheless, mainframe vendors contend that many companies want to use their big iron for cloud computing. In a CA Technologies-sponsored survey of 200 U.S. mainframe executives last fall, 73% of the respondents said that their mainframes were a part of their future cloud plans.

And IBM has been promoting mainframes as cloud platforms for several years. The company's introduction last year of the zEnterprise, which gives organizations the option of combining mainframe and distributed computing platforms under an umbrella of common management, is a key part of IBM's strategy to make mainframes a part of the cloud, say analysts.

The company set the stage 10 years ago when it gave all of its mainframes, zSeries S/390 and beyond, the ability to run Linux. While mainframes had been virtualizing for 30 years, since the introduction of the z/VM Virtual Machine operating system, once IBM added Linux you could run virtual X86 servers on a mainframe.

Over the last several years, some organizations have done just that, consolidating and virtualizing X86 servers using Linux on the mainframe. Once you start doing that, you've got the basis for a private cloud.

"You have this incredibly scalable server that's very strong in transaction management," says Judith Hurwitz, president and CEO of Hurwitz & Associates, an IT consultancy in Needham, Mass. "Here's this platform that has scalability and partitioning built in at its core." Plus, the mainframe's strongest assets -- reliability, availability, manageability and security -- are the very characteristics that companies are most concerned about as they consider rolling out major business applications in the cloud, she says.

Provisioning is the sticking point

But that lack of support for self provisioning is glaring. "The mainframe is very well controlled in most organizations, often to the point where it's locked in a room and people can't access it," says Julie Craig, an analyst specializing in application management at IT consultancy Enterprise Management Associates. "[Mainframe vendors] are going to have to do some developing to allow the self-service features of the cloud."

Reed Mullen, IBM's System z cloud computing leader, says that the lack of self provisioning is cultural, not technological. Companies could enable self-provisioning in mainframes either by using IBM's Tivoli Service Automation Manager or through custom development, he says.

And yet, he acknowledges that such implementations would still depend on the IT department -- users wouldn't have full self-service autonomy. Specifically, mainframe systems with self-provisioning options would require a user to submit a request by e-mail, and IT would have to approve the request before the resources were provisioned, Mullen explains. This reflects the "old habits" of the mainframe world, he says. But he also notes that any kind of cloud implementation, including those on distributed systems, would include an approval process.

"I know the perception is that the user doesn't have to bother anybody in IT, I just have to point and click to get my service," he says. But in every cloud scenario, he adds, there's some kind of approval process, a way to prioritize the requests, even though that process may not "require human eyes."

As for the licensing costs, Mullen says that IBM's current generation, System z, has a little-used "on-off" feature, whereby mainframe administrators can turn a processor core on for a limited time, paying short-term day rates for IBM software, rather than buying an expensive annual license based on the number of processor cores. "We are looking at taking advantage of this infrastructure to make it even more suitable for a cloud environment where there is a lot of unpredictable usage," says Mullen.